On Wed, 5 Nov 1997 17:41:31 -0500 (EST) W0AH@aol.com writes:
SNIPS
>found that the homebrew 9:1 balun that KF7MD and I had built 2 years
>ago was
>not working. Removing the balun, I saw no change in signal strength
>level.
Be careful here Doug. The core material and the windings are very
important to good performance. Many of us have had excellent results with
a FT114-61 core and 16 turns #24 quadrifilar; that gives you the option
of isolating the Beverage from the feedline.
> Several of you suggested I use an MFJ antenna analyzer to analyze my
>beverage impedance with and without a balun. Duhh. I hadn't thought
>of
>that! I also checked out the ARRL handbook and the ON4UN's Low Band
>DXing on
>winding baluns.
The analyzer can be misleading since harmonic content confuses the
readings.
I found that my TX and a QRP Wattmeter ( Oak Hills WM-1) gave predictable
results that the MFJ could not duplicate. I run the TX at 10W and thru a
10dB Bird attenuator and the WM-1 on the 1W scale.
If you want to spend lots of time you can now play with the terminating
resistor value to obtain a truly aperiodic antenna.
> Last night, just before dark, I put a TV balun, one of those
>cheapy,
>6:1, 300 ohm balanced to 50 ohms unbalanced baluns at the end of my
>700'
>balun.
Those TV baluns usually are only good down to 20MHz or so.
Using the MFJ analyzer, my impedance went from very high to
>about 15
>ohms on 160M and 30 ohms on 80M. According to the analyzer, the SWR
>was
>very high, >10. Still, the cheapy TV balun increased the signal level
>over
>an S-unit at the receiver compared to no balun. It still was quite
>deaf at
>160M altho I did manage to hear and work IT7ZGY and DF2PY with it last
>night.
> It worked better on 75-80M, and the signal strengths of the Europeans
>was
>only down 2-3 S-units on the beverage compared to my Hytower vertical
>(condx
>were excellent on 75M last night) the way a good beverage should
>perform
>according to W8JI.
Figure on a worst case of -20dB compared to a full size vertical.
Depending on condx equal signal levels are not uncommon.
> Today, I wound an autotransformer (se p. 7-18 in Low Band DXing)
>on the
>large toroid core that previously had the balun KF7MD and I had built.
What is the core material ?
GL Carl KM1H
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